Editorials

Dopamine in oliguria

Renal failure often manifests as oliguria. Many therefore view oliguria as a sinister development that should be prevented or treated in the hope of avoiding renal failure. However, oliguria can be a normal physiological response and, in itself, is a poor predictor of acute renal failure.^{1 2} Nevertheless, dopamine infusions have gained popularity over the past 20 years as a means to prevent or treat oliguria.

Dopamine is usually infused at low to intermediate rates of 2-5 µg/kg/min. The perceived beneficial effects include increased cardiac output, improved renal perfusion, reduced tubular metabolic activity, diuresis, and natriuresis. Thus, dopamine is used in a variety of clinical settings to prevent or ameliorate renal injury or hasten restoration of renal function.^{3 4} Cardiac failure and fluid overload have also been considered as indications for dopamine, although tachyphylaxis may limit these potential benefits.⁴

Recently, there has been a greater focus on potential adverse effects.⁵ Arrhythmias and myocardial, gut, and peripheral vascular ischaemia are well described. Other potential harmful effects include dopamine induced diuresis in the presence of volume depletion, pulmonary hypertension, impaired hypoxic ventilatory responses, decreased gastric motility, increased metabolic rate, and increased weight loss. Dopamine also causes endocrine and immune dysfunction, with reduced secretion of growth hormone, prolactin, and dehydroepiandosterone.⁶

Reduced secretion of growth hormone may promote catabolism and impair immune responses. Hypoprolactinaemia and low dehydroepiandosterone also impair cellular immune responses as a result of reduced T cell proliferation and effects on T helper cells.^{6 7} Importantly, reduced cellular immune responses are strongly associated with sepsis related mortality in patients receiving intensive care after emergency surgery.⁸ Thyroid function is also impaired.

Other hidden costs include central venous cannulation with its attendant risks,⁹ the need for infusion and monitoring equipment, and increased nursing and medical supervision. The assumption that dopamine may be beneficial but will do no harm is questionable, and its use as prophylaxis means that many patients who are exposed will never benefit. Since it is impossible to balance benefits against risks from small explanatory trials, studies of clinical outcomes are vital to judge whether dopamine infusions confer net benefit as prophylaxis or as treatment for oliguric states.

Denton concluded that there was little good published evidence to support the use of low dose dopamine infusions to prevent acute renal failure in high risk patients or to ameliorate the clinical course of established acute renal failure.⁴ However, these outcome studies are very small with little power even for the surrogate outcomes,⁴ and potential benefits might be overlooked.¹⁰ Many are too small to address clinically meaningful outcomes such as the long term renal function, the need for renal replacement therapy, and survival.

The present uncertainty regarding the benefits and risks of dopamine infusions is surely unacceptable. This uncertainty cannot be resolved by using surrogate markers because they often fail to predict the overall effect on clinical outcome.¹¹ Observational studies are weakened by bias and confounding factors and cannot be relied on to resolve clinical controversies.¹² The time has come for large scale, randomised controlled trials to be funded and conducted in the various settings in which dopamine is used so that doctors can confidently identify when dopamine has a real and rational role.

Given our existing knowledge, any recommendations on the indications for low dose dopamine¹³ will inevitably be based more on opinion than evidence, but some guidance may be helpful. In our opinion, dopamine should not be used as a prophylactic agent except in specific situations in which there is some evidence of benefit.¹⁰ It should be reserved for individual clinical situations where its diuretic and inotropic properties might be of use. If there are side effects, or no beneficial effects, the infusion should be stopped.¹³ The need for a good evidence base to guide the rational use of dopamine is paramount.

Brian H Cuthbertson, Intavent clinical research fellow of the Association of Anaesthetists and Royal College of Anaesthetists,^a David W Noble, Consultant in anaesthesia and intensive care ^a

^a Department of Anaesthetics and Intensive Care, Aberdeen Royal Infirmary, Aberdeen AB25 2ZN

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